Update, sorry I didn't get back before have been away for most of Christmas.
Managed to sort it out - I put a static IP address in the netbook, I changed the channel on the routers and I changed the password on the router, all these things at once - and it worked so I'm assuming it was the IP address that did it? And since then he's been able to connect to any WIFI.
What a relief it was to be able to give it to him before he went off for a week at Christmas
Thanks for all your help as usual
x Hope you all had a good one and Happy New Year